Building and maintaining floors in perfect condition keeps on paying. Here are two examples of how to do it.
Designing, specifying and constructing a typical concrete industrial floor for a moderatesize distribution center can easily cost $1 million. Sometimes, building owners overlook the role of the floor in saving money.
A concrete floor with superior flatness and levelness characteristics—a superflat floor—can save millions over the life of the building. This kind of floor reduces the risk of vehicle and equipment maintenance, less-than-optimum inventory turns, shrink (inventory damage) and healthcare costs from worker injuries.
According to OSHA, lift truck operators can suffer back, neck, hand and arm pain caused by excessive vibrations generated by bumpy floors.
A concrete floor with a rough surface prohibits the rapid, safe movement of cargo. Lift truck operators must constantly judge the surface of the floor and adjust speed accordingly. Many times, operators drive vehicles backward or slow to a crawling speed to better spot floor defects.
In addition to allowing optimum vehicle speeds, superflat floors also reduce lift truck electrical and mechanical maintenance and the need for replacement parts, such as wheels. They also allow longer battery life.
Another way a superflat floor saves money relates to product putaway. Seemingly minor variations in floor flatness found in non-superflat floors increase the “fishing rod effect” of lift truck masts. Operators tend to have more trouble placing forks high up when the floor is bumpy. Therefore, they must use extreme caution when trying to place high-reach cargo on an uneven floor. The higher the mast height, the more pronounced the lean, and the more likely the lift truck is to strike the storage racks.
At rack heights of 60 feet, if a lift truck parks on a bump of only one-quarter of an inch, the static lean of the mast is nearly 12 inches. A typical very narrow aisle (VNA) distribution center operation has only six inches of clearance between the load and the racks. A common joint defect in the concrete floor can be as much as one-half of an inch.
For order picking, bumps in the floor force operators to lower the load to reduce mast sway when moving to another location, thus wasting valuable time.
Additionally, some lift truck manufacturers will not warranty new lift trucks unless the floor meets certain flatness and levelness specifications. Warranty repair costs are higher with inferior floors because most lift trucks do not have a suspension system or pneumatic tires. Any sudden height change in the floor—even as little as 1/16 of an inch—can cause wheels to become airborne at speed. This, in turn, can lead to frame stress-cracking from continuous dynamic cyclic flexing of the frame members.
Cost of Change
There are two ways to get a superflat floor—construct a new floor or grind the existing one. Which method to use depends on basic considerations:
• Ownership of the floor;
• Estimated length of time the superflat floor will be needed;
• Size of the floor surface.
For new construction, proper forming, placement and finishing of a superflat floor is a common approach. For a distribution center in operation, grinding existing floors to superflat tolerances is cost effective. The cost to grind varies, depending on the type of grinding and the method.
It’s relatively easy to calculate lost productivity from nonsuperflat floors. Assume a lift truck travels at full speed of 6.5 miles per hour, or about 9.5 feet per second. The required time to traverse to the end of a 300- foot-long aisle is approximately 31.5 seconds at full speed. Empirical data taken from F-min Profiler (for measurements of existing floors) indicates an average of approximately 10% of a typical aisle (about 12 areas of varying lengths) requires remedial grinding. The amount of grinding needed to meet the floor flatness specification is based on the aisle width and rack height above the floor.
Also, assume the lift truck driver has a load and must slow down for defective areas. This translates to about 1.5 seconds lost per defect. In this scenario, the lift truck wastes about 18 seconds in a typical 300- foot-long aisle.
Next, assume the cost per hour to operate the distribution center is around $100 per hour per lift truck ($15/hour, plus benefits, taxes, insurance, overhead, burden, etc.). Multiply 18 seconds by $0.28 per second ($100 per hour divided by 3,600 seconds per hour) to get $0.50 per run.
Now, consider the total possible number of runs in an eight-hour shift for one lift truck (about 729), multiplied by the lost money per run ($0.50), multiplied by the number of shifts per working day (three), multiplied by the number of days per year, and the results are startling. Each lift truck loses about $1,000 worth of productivity per three-shift day. Multiply $1,000 by 365 to equal an approximate $300,000 annual cost per lift truck.
Although it can be challenging to determine exact superflat floor specifications, type of grinding needed and costs to remedy bumpy floors, time spent with a qualified concrete consulting company before work begins is worth the effort.
Initial investments will be returned through increased throughput, vehicle operating time and productivity and decreased maintenance costs for vehicles, pallets, racks and operator fatigue.
This article was prepared by Ken S. Shoemaker, vice president of engineering, ALLFLAT Consultants Inc., Encinitas, Calif., owner of FACE Consultants Floor Profiling. It was edited by MHM staff editors.